By way of background, ventricular fibrillation is one type of tachyarrhythmia. It is an irregular uncoordinated action of the fibers of the heart muscle, which results in a failure of the heart to pump blood. Ventricular tachycardia is another type of tachyarrhythmia and is also an irregularity of the heart muscle, generally characterized by an abnormally fast and altered contraction pattern, which may in some instances itself lead to death in a few minutes. Supraventricular tachycardia occurs in the tissues of the heart above the ventricles, especially in the sinus node, atrium, the atrioventricular (AV) bypass tract, or in the AV node. Such tachycardias, especially ventricular tachycardia, are subject to being accelerated into ventricular fibrillation by a number of known factors and stimuli, and hence their existence poses a latent or overt threat to continued life.
The importance of the foregoing is that ventricular tachycardia may, and ventricular fibrillation does, result in cessation of adequate pump function of the heart and sudden cardiac death. This is the leading cause of death of humans in the United States.
Various therapeutic means for controlling tachyarrhythmias have evolved. These include pharmaceutical compounds and compositions for suppressing tachyarrhythmias, implantable antitachycardia devices, and mechanical surgical procedures for the resection of heart tissue. Cardiac mapping techniques conducted during sinus rhythm and/or during induced tachycardia have made possible the identification of specific zones of heart tissue which are the foci of tachyarrhythmias. Such foci occur in many portions of the heart tissue, varying from person to person, and in normal tissue as well as in diseased tissue. Thus, cardiac mapping is an almost necessary diagnostic technique preceding the use of the inventions described herein but must be performed on each patient on a case-by-case basis.
Although cardiac mapping greatly improved the identification of the location of the foci of tachyarrhythmias, thus improving the success of mechanical resection surgery, most such foci occur where mechanical resection is difficult or impractical to perform. Alternative means for the ablation of tissue containing tachyarrhythmia foci have been attempted, e.g., cryothermia, and electrical energy delivered by means of electrode-bearing catheters. However, the therapeutic efficacy of employing electrical energy for ablation of ventricular tachycardia is still subject to debate among surgeons and physicians.
Thus, an objective of the invention described herein is to furnish a process for ablation of heart tissue which can be visually and electrically guided, and which also may be employed on heart tissue in diverse locations which are not as readily resectable by any other single procedure.
The new process is for the control of tachyarrhythmias in living humans by ablating heart tissue in vivo from at least one site by exposing the heart tissue at the site to a laser beam having sufficient energy and for a sufficient time to create a focal lesion at such site. The site in question is within an area on the inner or outer surface of heart tissue which has been previously located by cardiac mapping as causing an arrhythmia. For example, the site may be on the inside or the outside of a heart's ventricle or atrium, or in the atrioventricular groove. The laser energy is transmitted and precisely directed to the selected site by means of an elongated thin optical fiber, and the laser energy is emitted in a series of short discrete pulses.
The invention also includes the process of employing laser energy transmitted through an elongated optical fiber and delivered in a series of short discrete pulses for making incisions through all or only a portion of heart tissue, in lieu of mechanical surgery employing a scalpel. Thus, in performing a ventriculotomy, the laser energy may be employed to cut through a wall of a heart.